1. Field of the Invention
The present invention relates to an image blur prevention apparatus which prevents image blur caused by hand fluctuation or the like in a camera, an optical apparatus, and the like.
2. Description of the Related Art
In current cameras, since exposure determining, focusing, and other operations important for photographing are all automated, even for persons unskilled in camera operation, a possibility of making a photographing failure is remarkably decreasing.
Moreover, in recent years, a system for preventing a hand fluctuation applied to a camera has been researched, and there are almost no factors for inducing photographers' photographing mistakes.
Here, the system for preventing the hand fluctuation will briefly be described.
The hand fluctuation of the camera during photographing is a vibration whose frequency is usually in the range of 1 Hz to 10 Hz. To allow photographs to be taken without any image blur even if such hand fluctuation is caused at the time of shutter release, as a fundamental concept, camera vibration by the hand fluctuation is detected, and a correction lens has to be displaced in accordance with a detected value. Therefore, to take photographs without causing any image blur even if camera fluctuation occurs, first, the camera vibration is exactly detected, and secondly, an optical axis change by the hand fluctuation needs to be corrected.
In principle, the detection of the vibration (camera fluctuation) can be performed by mounting onto the camera a blur detection device which is provided with a blur detection sensor for detecting acceleration, angular acceleration, angular speed, angular displacement, and the like and a calculation portion for appropriately calculating/processing an output of the sensor to correct the camera fluctuation. Then, based on detected information, correction means for decentering a photographing optical axis is driven to perform image blur suppression.
FIG. 31 is an appearance perspective view of a compact camera which has a blur prevention system, and the system has a function of performing blur correction for vertical and transverse camera fluctuations shown by arrows 42p and 42y relative to an optical axis 41.
Additionally, a camera main body 43 has a release button 43a, a mode dial 43b (including a main switch), a retractable strobe 43c, and a finder window 43d.
FIG. 32 is a perspective view showing an inner constitution of the camera shown in FIG. 31. The constitution is provided with a camera main body 44, correction means 51, a correction lens 52, and a support frame 53 for freely driving the correction lens 52 in directions shown by arrows 58p and 58y to correct the blurs of the directions shown by the arrows 42p and 42y of FIG. 31, and details will be described later. Blur detection devices 45p, 45y have an angular velocity sensor accelerometer or the like for detecting blur around axes as shown by arrows 46p and 46y, respectively, and the like.
Outputs of the blur detection devices 45p and 45y are converted via calculation devices 47p and 47y described later to driving target values of the correction means 51, which are transmitted to coils of the correction means 51 to perform the blur correction. Additionally, numeral 54 denotes a base plate, 56p and 56y denote permanent magnets, and 510p and 510y denote coils.
FIG. 33 is a block diagram showing details of the calculation devices 47p and 47y. Since the devices have similar constitutions, in the drawing only the calculation device 47p is used for description.
The calculation device 47p is provided with, as surrounded by a dot-dashed line, a DC cut filter 48p, a low-pass filter 49p, an analog/digital converting circuit (hereinafter referred to as A/D converting circuit) 410p, and a driving apparatus 419p, and as shown by a broken line, a camera microcomputer 411. Moreover, the camera microcomputer 411 is constituted of a memory circuit 412p, a differential circuit 413p, a DC cut filter 414p, an integral circuit 415p, a memory circuit 416p, a differential circuit 417p, and a PWM duty converting circuit 418p.
Here, the blur detection device 45p used is a blur gyro which detects a camera fluctuation angular speed. The blur gyro is driven synchronously when the camera main switch is turned on, and starts detecting the blur angular speed applied to the camera.
For an output signal of the blur detection device 45p, a DC bias component superimposed to the output signal is cut by the DC cut filter 48p constituted of an analog circuit. The DC cut filter 48p has a frequency property of cutting signals whose frequencies are 0.1 Hz or less, so that a hand fluctuation frequency range applied to the camera of 1 to 10 Hz is not influenced. However, with the property of cutting 0.1 Hz or less, there is a problem that it takes almost ten seconds from when a blur signal is transmitted from the blur detection device 45p until DC is completely cut. To solve the problem, by setting a time constant of the DC cut filter 48p to be small within, for example, 0.1 second from when the camera main switch is turned on (providing a property of cutting a signal with a frequency of, for example, 10 Hz or less), DC is cut for a short time of about 0.1 second. Thereafter, by setting the time constant to be large (providing a property of cutting only a frequency of 0.1 Hz or less), deterioration of a blur angular speed signal is prevented by the DC cut filter 48p.
An output signal of the DC cut filter 48p is appropriately amplified by the low-pass filter 49p constituted of the analog circuit in accordance with a resolution of A/D converting circuit 410p, while a high-frequency noise superimposed to the blur angular speed signal is cut. This prevents a reading error from being caused by noise of the blur angular speed signal during sampling of the A/D converting circuit 410p when the blur angular speed signal is transmitted to the camera microcomputer 411. Moreover, an output signal of the low-pass filter 49p is sampled by the A/D converting circuit 410p and transmitted into the camera microcomputer 411.
The DC bias component is cut by the DC cut filter 48p, but by the subsequent amplification of the low-pass filter 49p the DC bias component is again superimposed to the blur angular speed signal. Therefore, in the camera microcomputer 411 DC cutting needs to be performed again.
In this case, for example, the blur angular speed signal sampled 0.2 second after the camera switch is turned on is stored in the memory circuit 412p, and a difference between the stored value and the blur angular speed signal is obtained by the differential circuit 413p to perform DC cutting. Additionally, since in the operation the DC cutting can only be roughly performed (because the blur angular speed signal, stored 0.2 second after the camera main switch is turned on, includes not only DC component but also actual hand fluctuation), in a later stage a sufficient DC cutting is performed by the DC cut filter 414p constituted of a digital filter. A time constant of the DC cut filter 414p can also be changed in the same manner as the analog DC cut filter 48p. For further 0.2 second after 0.2 second time periods elapsed after turning on of the camera main switch, the time constant is gradually increased. Specifically, when 0.2 second elapses from the turning-on of the main switch, the DC cut filter 414p has the filter property of cutting the frequency of 10 Hz or less. Thereafter, every time 50 msec elapse, the frequency to be cut by the filter is lowered to 5 Hz, 1 Hz, 0.5 Hz, and 0.2 Hz.
However, during the above-described operation, if the photographer depresses the release button 43a half way (turns on sw1) to perform photometry, or distance measurement, photographing may immediately be performed. In this case, it is unfavorable to consume time to change the time constant. Therefore, in such a case, the changing of the time constant is discontinued in accordance with photographing conditions. For example, when as a photometry result a photographing shutter speed is found to be 1/60, and a photographing focal distance is 150 mm, blur prevention precision is not particularly demanded. Therefore, time constant changing is completed when the DC cut filter 414p is given the property of cutting the frequency of 0.5 Hz or less (the change amount of the time constant is controlled by a product of the shutter speed and the photographing focal distance). Thereby, the time of the time constant changing can be shortened, and priority can be given to a shutter chance photo-opportunity. Naturally, with a faster shutter speed, or a shorter focal length, the time constant changing is completed when the DC cut filter 414p is given the property of cutting the frequency of 1 Hz or less. On the other hand, with a slower shutter speed, or a longer focal distance, photographing is inhibited until the time constant is completely changed to the end.
In response to the half depressed camera release button 43a (sw1 on), the integral circuit 415p starts integrating output signals of the DC cut filter 414p to convert the angular speed signal to an angular signal. However, as described above, when the time constant changing of the DC cut filter 414p is not completed, the integrating operation is not performed until the completion of the time constant changing. Additionally, as omitted from FIG. 33, the integrated angular signal is appropriately amplified on the basis of the focal distance, and subject distance information of that time, and converted in such a manner that the correction means 51 is driven by an appropriate amount in accordance with a blur angle (this correction is necessary because a photographing optical system is changed by zoom focus, and an optical axis eccentric amount changes relative to the driven amount of the correction means 51).
When the release button 43a is completely depressed (sw2 on), the correction means 51 starts to be driven in response to the blur angular signal. At this time, it needs to be noted that the correction means 51 should not start its blur correcting operation rapidly. As countermeasures, the memory circuit 416p and the differential circuit 417p are provided. The memory circuit 416p stores the blur angular signal of the integral circuit 415p in synchronization with the completely depressed release button 43a (sw2 on). The differential circuit 417p obtains a difference between the signal of the integral circuit 415p and the signal of the memory circuit 416p. Therefore, when the switch sw2 is turned on, two signal inputs of the differential circuit 417p are equal to each other, and a driving target value signal of the differential circuit 417p for the correction means 51 is zero, but thereafter outputs are continuously emitted from zero (the memory circuit 416p has a function of returning to its origin an integral signal at the time of the turning-on of the switch sw2). This prevents the correction means 51 from being abruptly driven.
The target value signal from the differential circuit 417p is transmitted to the PWM duty converting circuit 418p. By applying to the coil 510p of the correction means 51 (see FIG. 32) a voltage or a current corresponding to the blur angle, the correction lens 52 is driven in accordance with the blur angle, but PWM driving is preferable to save drive power consumption of the correction means 51 and power of a coil driving transistor.
For this purpose, the PWM duty converting circuit 418p changes coil driving duty in accordance with the target value. For example, in PWM having a frequency of 20 KHz, when the target value of the differential circuit 417p is "2048", the duty is changed to "0". When the value is "4096", the duty is changed to "100". Then, an interval between them is divided into equal parts and the duty is determined in accordance with the target value. Additionally, the duty determination is finely controlled not only by the target value, but also camera photographing conditions at that time (temperature, camera posture, power supply state) so that precise blur correction can be performed.
An output of the PWM duty converting circuit 418p is transmitted to the known driving apparatus 419p such as PWM driver, and an output of the driving apparatus 419p is applied to the coil 510p of the correction means 51 (see FIG. 32) to perform the blur correction. The driving apparatus 419p is turned on in synchronization with the turning-on of the switch sw2, and turned off when exposure to a film is completed. Moreover, even upon completion of the exposure, as long as the release button 43a is half depressed (sw1 on), the integral circuit 415p continues integrating. When the switch sw2 is next turned on, the memory circuit 416p again stores a new integral output.
When the half depressed release button 43a is released, the integral circuit 415p stops integrating the outputs of the DC cut filter 414p, and resetting of the integral circuit 415p is performed. The reset means that information integrated by that time is all emptied.
When the main switch is turned off, the blur detection device 45p is turned off, thereby ending the blur prevention sequence.
Additionally, when the output signal of the integral circuit 415p is larger than a predetermined value, it is judged that the camera has been panned, and the time constant of the DC cut filter 414p is changed. For example, the property of cutting the frequency of 0.2 Hz or less is changed to the property of cutting 1 Hz or less, and the time constant is returned to the original in the predetermined time. The time constant change amount is also controlled by the size of the output of the integral circuit 415p. Specifically, when the output signal exceeds a first threshold, the property of the DC cut filter 414p is changed to the property of cutting 0.5 Hz or less. When the signal exceeds a second threshold, the property is changed to the property of cutting 1 Hz or less. When the signal exceeds a third threshold, the property is changed to the property of cutting 5 Hz or less.
Moreover, when the output of the integral circuit 415p becomes very large, the integral circuit 415p is once reset to prevent calculation overflow.
In FIG. 33, the DC cut filter 414p is constructed to start its operation 0.2 second after the main switch is turned on, but is not limited, and the operation may be started when the release button 43a is half depressed. In this case, when the time constant changing of the DC cut filter is completed, the integral circuit 415p is operated.
Moreover, the integral circuit 415p also starts its operation when the release button 43a is half depressed (sw1), but may be constructed to start its operation when the release button 43a is completely depressed (sw2). In this case, the memory circuit 416p and the differential circuit 417p become unnecessary.
In FIG. 33, the DC cut filter 48p and the low-pass filter 49p are disposed in the calculation device 47p, but needless to say they may be disposed in the blur detection device 45p.
FIGS. 34 to 36 are views showing details of the correction means 51. Specifically, FIG. 34 is a front view of the correction means 51, FIG. 35A is a side view as seen from a direction of arrow 35A of FIG. 34, FIG. 35B is a sectional view taken along 35B--35B of FIG. 34, and FIG. 36 is a perspective view of the correction means 51.
In FIG. 34, the correction lens 52 (as shown in FIG. 35B, the correction lens 52 comprises two lenses 52a and 52b fixed to the support frame 53, and a lens 52c fixed to the base plate 54, to constitute a photographing optical system group) is fixed to the support frame 53.
To the support frame 53 a yoke 55 of a ferromagnetic material is attached, and to a back surface of the yoke 55 of the drawing, the permanent magnets 56p and 56y of neodymium are adsorbed/fixed (as shown by hidden lines). Moreover, three pins 53a radially extended from the support frame 53 are engaged in elongated holes 54a formed in a side wall 54b of the base plate 54.
As shown in FIGS. 35A and 36, the pin 53a is engaged in the elongated hole 54a in a direction of an optical axis 57 of the correction lens 52 without any looseness. However, since the elongated hole 54a extends in a direction orthogonal to the optical axis 57, the support frame 53 is inhibited from moving in the direction of the optical axis 57 relative to the base plate 54, but can freely move in a plane orthogonal to the optical axis (arrows 58p, 58y, 58r). However, as shown in FIG. 34, since tensile springs 59 are extended between hooks 53b on the support frame 53 and hooks 54c on the base plate, the frame is elastically regulated in each direction (58p, 58y, 58r).
To the base plate 54, the coils 510p, 510y are attached opposite the permanent magnets 56p, 56y (partially hidden lines). The yoke 55, the permanent magnet 56p, and the coil 510p are arranged as shown in FIG. 35B (the permanent magnet 56y and the coil 510y are arranged in the same manner). When an electric current is passed through the coil 510p, the support frame 53 is driven in the direction of arrow 58p. When current is passed through the coil 510y, the support frame 53 is driven in the direction of arrow 58y.
Additionally, the driving amount is obtained by a balance of a spring constant of the tensile spring 59 in each direction and a thrust generated by association of the coil 510p, 510y and the permanent magnet 56p, 56y. Specifically, based on an amount of currents passed through the coil 510p, 510y, the eccentric amount of the correction lens 52 can be controlled.
As described with reference to FIG. 33, for the signal of the blur detection device 45p (45y), the DC bias component superimposed on the signal is cut by the DC cut filter 48p constituted of the analog circuit. As shown in FIG. 37, the DC cut filter 48p is constituted of an operation amplifier 420p, a capacitor 421p, resistances 422p, 423p and a switch 424p (DC cut filter of the blur detection device 45y is constituted in the same manner). To set the property of the DC cut filter 48p to the property of cutting the frequency of 0.1 Hz or less, for example, the capacitor 421p is set to 10 .mu.F, and the resistance 422p is set to 160 k.OMEGA..
Additionally, a resistance value of the resistance 423p is set, for example, to 1.6 k.OMEGA.. In this case, when the switch 424p is closed, the DC cut filter 48p cuts the frequency of 10 Hz or less. When the switch 424p is opened, the filter has the property of cutting the frequency of 0.1 Hz or less. Therefore, as described above, by closing the switch 424p until, for example, 0.1 second has elapsed from the turning-on of the camera main switch, the DC component can be cut in an early stage.
Furthermore, in the circuit constitution of FIG. 37, since a large-capacity capacitor of 10 pF is used in the capacitor 421p, the circuit is remarkably enlarged, and a problem arises that costs are raised. Furthermore, when the DC cut filter 48p is constituted in this manner, another problem arises that the blur prevention precision is lowered. This respect will be described with reference to FIGS. 38A and 38B.
FIGS. 38A and 38B conceptually show the frequency property of the DC cut filter 48p of FIG. 37, a line segment 425 shows a ratio (gain) of an output signal relative to a signal which is transmitted to the DC cut filter 48p, and a line segment 426 likewise shows a phase of the signal to be output relative to the input signal.
Referring to the line segment 425, the gain decreases at frequencies below 0.1 Hz, whereby signal outputs of 0.1 Hz or less are attenuated, and DC cut property can be obtained.
In order to precisely prevent blur, the signal of the blur detection device needs to be transmitted to the correction means without any phase deviation, if possible. Referring to the line segment 426, in a hand fluctuation frequency range of 1 to 10 Hz, particularly on a low frequency side, the phase advances, and the blur cannot precisely be prevented.
To enhance the blur prevention precision, for example, the current property of the DC cut filter which cuts the frequency of 0.1 Hz or less may be changed to the property of cutting 0.01 Hz. In this case, however, the capacity of the capacitor 421p needs to be increased, for example, to 100 .mu.F (or the resistance 422p needs to be increased to 1.6 M.OMEGA.), which is unfavorable also considering from a circuit scale, and a noise respect.
As described above, the current DC cut filter has problems that the capacitor is large and unsuitable for miniaturization and cost reduction and that the blur prevention precision is lowered.
One of objects of the present invention is to provide a blur prevention apparatus which is reduced in size and weight, which removes an offset signal superimposed on a blur detection signal in accordance with a state of the blur prevention apparatus and a state of an apparatus on which the blur prevention apparatus is mounted, and which can output a highly precise blur detection signal.